This invention relates to an apparatus for refining brine including calcium and magnesium ions.
An ion exchange membrane method or the like has been used widely to produce sodium hydroxide by electrolyzing raw brine such as raw salt dissolved in water. In general, raw brine includes impurities such as calcium ions, magnesium ions and the like. Therefore, it is required to remove the impurities and refine the raw brine before the electrolysis of the raw brine. For this purpose, sodium hydroxide and sodium carbonate are added to the raw brine to crystalize the calcium and magnesium ions. The resulting calcium carbonate and magnesium hydroxide particles are condensed into the form of flocks in the presence of a high molecular condensate. The resulting raw solution is introduced into a settling tank where the flocks are settled and separated from the supernatant solution. However, the flocks have a specific gravity substantially the same as the specific gravity (1.2) of saturated brine and drift in the settling tank with convection currents caused by a great difference between the temperature of the solution surface from which heat is radiated to the atmosphere and the temperature of the solution at the bottom of the setting tank. The residence time required for the flocks to sink and separate from the raw solution is as long as six to ten hours. It is the current practice to improve the brine refining efficiency by increasing the size of the settling tank. However, this results in a space consuming brine refining apparatus.